Thermal expansion/contraction between cooler and chip itself "pumps" out the thermal paste which over time degrades cooling performance. If the system is running 24/7 its probably not as noticeable because you don't get the frequent heating/cooling you'd see on a device that gets power cycled often.
Nothing a repaste job wont fix.
Edit: to answer my own question it looks like Apple uses thermal paste but the cooling in the M2 MacBook Air looks extremely flimsey to the point of being almost non-existent. I doubt it will be affected much at all by this.
E.g. https://thermalmanagement.honeywell.com/us/en/products/therm...
Yes. Glue. Paste is for when you might want to one day separate part from heatsink. If you don't care about repairs, it is perfectly reasonable to just glue them together with thermal adhesive.
That is already available and used in some Laptops. Look up Honeywell thermal pad.
The problem is as always, cost.